French Pat. No. 1 253 881 discloses a washer of refractory fibre to be placed on the cold portion of the insulator adjacent the portion which is actually embedded and which becomes hot during casting. The washer is intended to reduce the thermal shock during casting.
Also, in the case of a cap-and-rod insulator made of hardened glass, it is known via French patent No. 2 209 987 to fit a metal ring on the head of the dielectric which ring can act as a seal between the mould of the cap and the skirt of the dielectric. Said ring is advantageously made of the same substance as the cap.
The appearance of cracks between the body of the cap and the above-mentioned ring have been observed. These cracks are ugly and, more particularly, dangerous, since they promote corrosion.
Preferred implementations of the present invention mitigate these disadvantages.